The titania composite membrane of the present invention has excellent properties such as thermal stability, mechanical strength and good perm-selectivity for water molecule in water/alcohol mixtures due to the hydrophilic property of the titania surface layer, thus being applicable to a membrane for separating water/alcohol mixtures.
In preparation of water-permeable separation membrane, a pervaporation technique using a polymeric membrane is conventionally used. Compared with other separation and purification techniques, the pervaporation technique using a polymeric membrane has an advantage of low energy consumption, but has a serious limitation in application temperature due to the intrinsic property of polymer. That is, in case of water-permeable membrane prepared by using polymer, there is a problem that application temperature is limited because the polymer chain flows and the membrane becomes unstable at high temperature due to the intrinsic property of polymer. On the other hand, in case of an inorganic membrane where the surface layer is calcined to optimize the performance and then has thermal stability, the limitation of the application temperature may be easily overcome.
Therefore, recent studies have been focused on the use of the inorganic membrane instead of the polymeric membrane. Also, sol-gel process has been explored for preparing inorganic membrane since it requires a simple process and a simple device. To make the inorganic membrane stand comparison with the polymeric membrane, it is required to increase the perm-selectivity performance by preparing the inorganic coating layer having a uniform pore distribution and a high microporosity. It is important to prepare a stable sol with small particle size because the properties of the inorganic coating layer are originated from the properties of a sol that forms the coating layer.
In case of the titania as a material of inorganic membrane, however, it is difficult to control its properties because the reactivity for water is much contrary to silicate [R. R. Bhave, Inorganic membranes: synthesis, Characteristics and Applications; Ch. 2 (1991), Burggraaf et al., Proceedings of the Second International Conference on Inorganic Membrane (1991) p. 37, A. J. Burggraaf et al., J. Mater. Sci., 27 (1992) 1023-1035, M. A. Anderson et al., J. Am. Chem. Soc., 77 (1994) 1939-1945].
Accordingly, for preparing a titania separation membrane by sol-gel method, it is essential to reproducibly prepare the titania sol with excellent property and stability, thereby preparing a thin layer.
The present inventors have conducted extensive studies to prepare the titania separation membrane with thermal stability at high temperature and a good perm-selectivity for water molecule even at high temperature. As a result, they found a fact that thermal stability of the separation membrane can be ensured by sequentially modifying macropores of a porous support with silica xerogel and γ-alumina sol in this order and water can be separated effectively from water/alcohol mixtures due to the excellent hydrophilicity of the titania surface layer by coating the titania sol with small and uniform particles by soaking-rolling method.
Therefore, the object of the present invention is to provide a titania composite membrane for separating water/alcohol mixtures having an excellent thermal stability at high temperature and a method of preparing the same.